The plant immune system recognizes pathogens early in the infection process, activating immune responses capable of arresting them before they colonize and establish themselves as a threat to viability. Pathogens that survive this first line of defense are met by a second line of defense that results in a higher amplitude programmed cell death response, which effectively sequesters some pathogens in foci of dead cells. However, in the case of necrotrophic pathogens, the class of plant pathogens that acquire nutrients from dead tissue, this defense response is hijacked and utilized by the pathogen to further disease proliferation, translating to crop failure. The project will fill knowledge gaps in the understanding of how plants perceive this important class of pathogens and how immunity responses result in a positive outcome for the plant host (disease resistance). Thus, the project will contribute to understanding of how plant immunity responses are effective at stopping the necrotrophic pathogens which is important as they are becoming well known for their roles in causing disease on important crops and are significantly contributing to world food security issues. The information generated will transect multiple pathosystems important to crop production through characterizing and defining the mechanism that regulates host signaling and immunity against diverse pathogens. The molecular genetic and genomic data generated and molecular tools developed, will broadly benefit the plant-microbe interactions scientific community as well as answer fundamental questions that will facilitate the deployment of genetic resistance in crops contributing to a more secure food supply. This research will also be used in cross-disciplinary training of high school, undergraduate, graduate, and post-graduate students in molecular genetics and molecular plant pathology from both the host and pathogen perspective. A collaborative outreach program developed through this grant will involve education of young Native American scientists in order to effectively recruit them into the scientific fields effectively broadening the participation of the most under represented group in the STEM fields.<br/><br/>The overarching hypothesis is that early immunity responses are effective at stopping the necrotrophic pathogens, yet later elicited immunity responses result in programmed cell death that is effectively hijacked by the necrotophic specialists to complete their lifecycle, contributing to disease susceptibility. The two specific objectives to test this hypothesis focus on a comprehensive evaluation of the temporally and spatially distinct immunity and virulence responses from the host (barley) and pathogen (Pyrenophora teres f. teres), respectively. These aims will address fundamental questions: 1) is a diverse receptor-like protein targeted by multiple necrotrophic effectors to elicit necrotrophic effector triggered susceptibility (NETS); and 2) does a highly effective dominant resistance gene activate early defense responses, arresting the necrotrophic specialist before it colonizes and deploys its necrotrophic effector repertoire? The first component of the plant immune system investigated is a highly variable receptor-like protein, Spt1, which is targeted by multiple diverse necrotrophic effectors located throughout the genomes which evolved to incite disease. This receptor contains unprecedented variability at a localized region that correlates with specific susceptibilities, suggesting that the pathogen populations continually evolved to target this unknown domain and the host has been undergoing a high level of diversifying selection at this domain to evade pathogen virulence. The information gathered on the receptor and necrotrophic effectors will fill fundamental gaps in the knowledge of how necrotrophic specialists target the host and manipulate a weak link in its immune system to cause disease.<br/><br/>This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.